Large-format inorganic light-emitting diode (iLED) displays are used in outdoor and stadium displays. Because the iLEDs are relatively large, for example one square millimeter, they are restricted to relatively low-resolution displays. However, as iLED technology develops, there is increasing interest in applying smaller iLEDs to displays having higher resolution. Full-color displays typically include pixels with three (or more) emitters, usually red, green, and blue emitters, distributed in an array over the display surface.
Inorganic light-emitting diodes are semiconductor light sources relying on p-n junctions to emit light when a suitable voltage is applied across the light-emitting diode. The color of the light emitted from the iLED corresponds to the energy bandgap of the semiconductor. Thus, different semiconductor materials can produce different colors of light when stimulated with suitably different voltages. Typical materials include InGaN (emitting blue light), AlGaP (emitting green light), and AlGaAs (emitting red light), among many other materials. Blue-light-emitting materials can emit light at voltages ranging from 2.5-3.7 volts, green-light-emitting materials can emit light at voltages ranging from 1.9-4 volts, and red-light-emitting materials can emit light at voltages ranging from 1.6-2 volts.
In order to provide the different voltages needed by the different light-emitting diodes emitting different colors of light in a full-color pixel, a separate power supply can be supplied to each color light emitter in each multi-color pixel. By supplying the appropriate voltages to each light emitter, the light emitters efficiently emit light. However, providing three (or more) different voltage power signals to each multi-color pixel requires three times as many power supplies, lines, and connections, reducing the available space in the display and increasing costs.
Alternatively, a single power supply can be provided to all three different iLEDs in the full-color pixels. In this case the excess voltage is dropped across other circuit components, increasing heat and reducing overall display system power efficiency.
There is a need, therefore, for an improved pixel structure that improves power efficiency and reduces wiring overhead.